Binding of empty string is inconsistent between reflection and source generator configuration binders

[svick]

The following tests fail for the source generated configuration binder, but succeed for the reflection binder, showing inconsistencies between the two binders. I think these should be fixed. It's likely that some fixes will require changing the source generator, and others changing the reflection binder. (In other words, one of these tests succeeding doesn't necessarily mean it's the correct behavior.)

[Fact]
public void GetValue_EmptyStringForString_ReturnsEmptyString()
{
    IConfiguration config = TestHelpers.GetConfigurationFromJsonString("""{ "Value": "" }""");

    Assert.Equal(string.Empty, config.GetValue<string>("Value"));
}

[Fact]
public void GetValue_EmptyStringForInt32_Throws()
{
    IConfiguration config = TestHelpers.GetConfigurationFromJsonString("""{ "Value": "" }""");

    Assert.Throws<InvalidOperationException>(() => config.GetValue<int>("Value"));
}

[Fact]
public void GetValue_EmptyStringForByteArray_ReturnsEmptyArray()
{
    IConfiguration config = TestHelpers.GetConfigurationFromJsonString("""{ "Value": "" }""");

    Assert.Empty(Assert.IsType<byte[]>(config.GetValue<byte[]>("Value")));
}

[Fact]
public void Get_EmptyStringForNullableInt32_ReturnsNull()
{
    IConfiguration config = TestHelpers.GetConfigurationFromJsonString("""{ "Value": "" }""");

    Assert.Null(config.GetSection("Value").Get<int?>());
}

[Fact]
public void Get_EmptyStringForInt32_ThrowsConversionException()
{
    IConfiguration config = TestHelpers.GetConfigurationFromJsonString("""{ "Value": "" }""");

    Assert.Throws<InvalidOperationException>(() => config.GetSection("Value").Get<int>());
}

[Fact]
public void Get_EmptyStringArrayElementWithErrorOnUnknownConfiguration_Throws()
{
    IConfiguration config = TestHelpers.GetConfigurationFromJsonString("""{ "Values": [ "" ] }""");

    Assert.Throws<InvalidOperationException>(
        () => config.GetSection("Values").Get<int[]>(o => o.ErrorOnUnknownConfiguration = true));
}

[Fact]
public void Get_EmptyStringDictionaryValueWithErrorOnUnknownConfiguration_Throws()
{
    IConfiguration config = TestHelpers.GetConfigurationFromJsonString("""{ "Values": { "Key": "" } }""");

    Assert.Throws<InvalidOperationException>(
        () => config.GetSection("Values").Get<Dictionary<string, int>>(o => o.ErrorOnUnknownConfiguration = true));
}

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